A major limitation of any apparatus for screening materials such as for example aggregates, waste, wood, recyclable materials, glass, sand, concrete, asphalt, demolition debris, etc., is the throughput of screened material that can be processed per unit of time. This is true of apparatus such as found in U.S. Pat. Nos. 6,237,865 and 7,506,461 that employ screening shafts for example. As described therein, a screening shaft defines an elongated rotatable shaft. Replaceable fixed elements project radially away from the surface of the circumference of the screening shaft. Each screening shaft is rotatable about its longitudinal axis, and the rotation is powered so that it is driven under the control of the operator. Several of the screening shafts are disposed in alignment with each other across the outlet area of the bucket containing the screening shafts. The screening size can be varied depending on the radial length of the elements from the surface of the shaft. U.S. Pat. Nos. 6,237,865 and 7,506,461 disclose buckets that load from the front, have solid bottoms and sides and have multiple screening shafts aligned in a row at the back of the bucket and lying in a plane that is disposed at a 90 degree angle from the bottom of the bucket.
U.S. Pat. No. 5,581,916 also discloses a bucket that loads from the front and has solid sides, but has a solid back and has a reciprocating screen in the bottom of the bucket. The direction of reciprocation of the screen is front to back. The reciprocating motion of the screen is driven by a motor that is mounted on the bucket and thus provides a reciprocating connection between the screen and the bucket.
However, the buckets described above require additional machines to bring to the buckets from other sites the raw materials that are to be screened, can only be fed from one direction, and become clogged by debris above a predetermined larger size and so must stop operating while such debris is cleared. Accordingly, these limitations in turn limit the throughput that can be attained by these screening apparatus.
Devices that are essentially mechanical shovels are known. U.S. Pat. No. 5,160,034 discloses a front-end loader with a shovel attachment having a vibrating screen forming the bottom of the shovel. The shovel takes up sand as the screen slides beneath about a two inch depth of the sand as the front-end loader moves forward. The screen is vibrated to separate the sand from the oversized material, which remains in the shovel. However, this device must be moving forward to take up sand and only can be loaded from the front. Accordingly, this vibrating screen in the bottom of the shovel attachment is not suitable for processing large volumes of material.
Moreover, the screen media itself typically is formed of a steel plate that typically is about ⅜ inches thick, and holes are punched through this thickness of the plate to allow material smaller than the area of the hole to pass through the screen media. Another type of screen media typically is formed of a sheet of solid rubber or urethane that is about one inch thick and has holes punched through this thickness of the sheet. This sort of screen media is needed to withstand the rigors of screening the heavy materials involved. However, because of the need to punch the openings to create this sort of screen media, the fineness of the particulates that can be passed through such openings tends to be commensurately limited. Both types of this screen media typically are bolted to supports that are in turn bolted to a screen box that is open only at the top and at the bottom of the vibrating screen, and the entire screen box is shaken to facilitate the filtering function of the vibrating screen.